10 Lessons from the Field: Designing a Passive House that Works

Designing a Passive House is both thrilling and humbling. On paper, the principles look straightforward: airtightness, insulation, thermal bridge-free design, high-performance windows, and a balanced ventilation system. But when theory meets the jobsite, you quickly discover how many variables can throw your targets off course.

This article reflects on a real Passive House project currently under construction in the Del Ray neighborhood of Alexandria, Virginia. It’s a large, single-family residence aiming for PHIUS certification. I had the pleasure of sharing the journey during a recent AIA Potomac Valley webinar. The house is still taking shape, but the lessons are already clear.

Here are 10 takeaways from the field, for any architect considering a Passive House project:

1. Bring the Whole Team On Early

MEP engineers, structural engineers, landscape architects, and especially your Passive House consultant should all be at the table from the start. Waiting too long means missed opportunities to align design intent with certification requirements.

2. The Site Is the Site. Design with Its Constraints.

Our lot orientation meant that the backyard—where the family wanted open, expansive glazing—faced north. That single decision had ripple effects across energy models, window performance, and cooling loads.

3. Clarify What Passive House Really Means

It’s not passive solar. It’s not just good insulation. Passive House is a rigorously modeled system that demands precision. Expect surprises. For us, cooling loads nearly pushed us over the edge.

4. There Are More Standards Than PHIUS

We also pursued EPA Indoor airPLUS and local code requirements, which layered in additional criteria for indoor air quality, materials, and ventilation.

5. ERVs and Ductwork Demand Early Coordination

Dual systems for heating/cooling and ventilation must be planned well in advance. Duct routing, sealing, and insulation are make-or-break moments.

6. Air Sealing is an Art Form

Our first blower door test failed. Not even close. But with patience, rework, and eventually AeroBarrier, we hit 0.22 ACH—beating the 0.60 PHIUS threshold. It took a whole team and a willingness to find leaks anywhere—even around spiderwebs.

7. Grade 1 Insulation is Non-Negotiable

Compression, gaps, and paper-faced batts were all issues. It took three passes (and the GC doing it themselves) to get insulation right. Next time: a mock-up wall and training upfront.

8. Watch for Thermal Bridges Beyond Windows

Steel beams, exposed fasteners, and cantilevered elements all carry hidden risks. Our curtain wall and support fins required special attention and custom modeling to ensure performance.

9. Triple-Pane Windows Help, But Install Matters More

Even high-end windows fail if sashes aren’t properly seated or seals aren’t tight. We saw air leakage through a sash during blower door testing. Align everyone to the "why" of Passive House, not just the specs.

10. Intent is Everything

Our success hinged on collaboration, humility, and trust. The builder, consultant, owner, and design team were all aligned on the vision. Mistakes happened—but we fixed them together.

Bonus: A Word from the Homeowner

"This has been one of the most exciting projects of my life," said homeowner Duncan Cohen. "The performance is extraordinary, but so is the comfort, the quiet, and the intentionality. We’re designing a home that we can age in, live in, and feel good in—for decades."

Deborah Buelow, AIA, is the founder of Cedar Architecture, a boutique regenerative design firm based in Alexandria, Virginia. Cedar leads the transition to a built environment that gives back more than it takes. We craft beautiful, high-performing spaces that seamlessly reconnect people with nature.